1. Field of the Invention
The present invention relates to a semiconductor memory device. For example, the present invention relates to a semiconductor memory device comprising memory cells each having a charge accumulation layer and a control gate.
2. Description of the Related Art
Electrically erasable and programmable ROMs (EEPROMS) are known as nonvolatile semiconductor memories that allow data to be electrically rewritten. NAND flash memories are known as EEPROMs for which the capacity and integration degree can be increased.
An increasing number of voltage types have been required for the recent NAND flash memories which have reduced sizes and use multi-level data. For example, when data is written, plural types of voltages need to be applied to unselected word lines. A configuration using a plurality of voltages is described in, for example, U.S. Pat. No. 7,088,620.
However, an increase in the number of voltage types or in the number of variations in a load on a charge pump circuit that generates voltages increases the number of charge pump circuits and the number of charge pump circuit types. This also makes it difficult to control the charge pump circuit.